The script wrote the hook to .git/hooks, which fails when .git is a
file rather than a directory, as in a clone made with
--separate-git-dir. It now asks git for the repository's own git
directory with `git rev-parse --git-common-dir`, creates its hooks
directory if missing, and writes the hook there. In an ordinary clone
that is .git/hooks, so nothing moves. Before writing anything it stops
with an error when its top directory is not the top of the checkout
git finds, so a copy inside another repository cannot replace that
repository's hook. git's core.hooksPath setting is not followed; where
it is in force, git does not run the installed hook, as before.
Model: opus-5-5